Cytochrome P450nor gene was cloned into the expression vector pET-28 to yield the recombinant expression plasmid pET-P450nor, which could direct the synthesis of a eukaryotic derived protein in Escherichia coli BL21. The vector allows overproduction and single-step purification of (His) 6-tagged cytochrome P450nor by the facilitation of metal (Ni 2+ ) chelate affinity chromatography. The expression level of cytochrome P450nor was high at 30℃ after IPTG induction. SDS-PAGE and Western blot analysis showed a specific band (about 43 kDa). The overproduced cytochrome P450nor was purified to electrophoretic homogeneity within 2.5 h and about 20.8 mg purified protein was obtained from 2 L cell culture. The proliferation of SSMC-7721 cell line could be inhibited by cytochrome P450nor. Rabbit polyclonal antibodies (titer over 64 000 ) were produced against recombinant cytochrome P450nor and proved to be very useful for immunoblotting study. Availability of this expression system and specific antibodies should facilitate characterization of the role of cytochrome P450nor in the metabolism of NO. Cytochrome P450nor gene was cloned into the expression vector pET-28 to yield the recombinant expression plasmid pET-P450nor, which could direct the synthesis of a eukaryotic derived protein in Escherichia coli BL21. The vector allows overproduction and single-step purification of (His) The expression level of cytochrome P450n was was at 30 ° C after IPTG induction. SDS-PAGE and Western blot analysis showed a specific band (about 43 kDa) . The overproduced cytochrome P450nor was purified to electrophoretic homogeneity within 2.5 h and about 20.8 mg purified protein was obtained from 2 L cell culture. The proliferation of SSMC-7721 cell line could be inhibited by cytochrome P450nor. Rabbit polyclonal antibodies (titer over 64 000 ) were produced by recombinant cytochrome P450nor and proved to be very useful for immunoblotting study. Availability of this expression system and s pecific antibodies should facilitate characterization of the role of cytochrome P450nor in the metabolism of NO.